This invention relates to the vehicle control.
JP-A-H11-82084 published by the Japanese Patent Office in 1999 discloses a vehicle drive system which adds a reserve drive power to a target drive power to calculate a minimum needed power, computes the engine rotation speed which can realize the minimum needed power with the best fuel cost-performance, and controls the speed ratio of a continuously variable transmission (CVT) so that the input rotation speed of the CVT becomes equal to the computed rotation speed.
In a vehicle comprising a CVT, as the drive point of the engine can be freely selected, fuel cost-performance can be improved by choosing a point with least fuel consumption among the drive points which generate a target drive power. On the other hand, when the drive point is close to a maximum torque line, torque cannot be generated immediately even if the accelerator pedal is depressed, and acceleration cannot be obtained unless the speed ratio of the CVT is moved to the low side (large speed ratio side) and the engine rotation speed is increased. Therefore the engine rotation speed is set high so that power can be increased immediately even if the CVT does not perform speed change when the accelerator pedal is depressed, and sufficient power must be reserved for acceleration (reserve drive power). Although this satisfies acceleration demand, conversely, in the steady state when there is no acceleration demand, the drive point shifts from the best fuel cost-performance point, and fuel cost-performance is impaired.
In order to solve this problem, with the above-mentioned conventional technique, the minimum needed power is computed by adding a reserve drive power according to the running condition to the target drive power, and the engine rotation speed is controlled to the rotation speed which generates this minimum needed power with the best fuel cost-performance. This realizes the required reserve drive power, and also prevents the drive point in the steady state without acceleration demand from shifting much from the best fuel cost-performance point.
However, in this method, the reserve drive power corresponds to the power from the actual drive point of the engine to the maximum needed torque. That is, a power corresponding to the difference from the best fuel cost-performance lane to the maximum torque line is obtained in reserve rather than the set reserve drive power, the drive point shifts by a corresponding amount to higher rotation speed, and fuel cost-performance is impaired.
It is therefore an object of this invention to suppress the drive point of an engine from shifting from the best fuel cost-performance line while maintaining a set reserve drive power.
In order to achieve above object, this invention provides a drive system for a vehicle, comprising an engine, a drive wheel, a continuously variable transmission provided between the engine and the drive wheel, a sensor which detects an accelerator depression amount, a sensor which detects a vehicle speed, a sensor which detects an engine rotation speed, and a controller functioning to compute a target drive power based on the accelerator depression amount and vehicle speed, set a reserve drive power for vehicle acceleration, compute a minimum needed power by adding the reserve drive power to the target drive power, compute a best fuel cost-performance rotation speed based on the target drive power and best fuel cost-performance power characteristics of the engine, compute a minimum needed rotation speed based on the minimum needed power and maximum power characteristics of the engine, compare the best fuel cost-performance rotation speed and minimum needed rotation speed, and select the larger as the target input rotation speed of the transmission, control the speed ratio of the transmission based on the vehicle speed and target input rotation speed, and control the torque of the engine based on the engine rotation speed and target drive power.
According to an aspect of this invention, this invention provides a vehicle drive system, comprising an engine, a drive wheel, a generator connected to the engine, a motor connected to the drive wheel, a battery electrically connected to the generator and the motor, a sensor which detects an accelerator depression amount, a sensor which detects a vehicle speed, a sensor which detects an engine rotation speed, a sensor which detects a motor rotation speed and a controller functioning to compute a target drive power based on the accelerator depression amount and vehicle speed, compute a required motor power by correcting the target drive power by the efficiency of the motor, set a target generated power according to the required motor power, compute a target engine power by correcting the target generated power by the efficiency of the generator, set a reserve drive power for vehicle acceleration, compute a minimum needed power by adding the reserve drive power to the target engine power, compute a best fuel cost-performance rotation speed based on the target engine power and best fuel cost-performance power characteristics of the engine, compute a minimum needed rotation speed based on the minimum needed power and maximum power characteristics of the engine, compare the best fuel cost-performance rotation speed and minimum needed rotation speed, and select the larger as the target rotation speed of the generator, control the torque of the motor based on the motor rotation speed and target drive power, control the rotation speed of the generator based on the target rotation speed, and control the torque of the engine based on the engine rotation speed and target engine power.
According to an another aspect of this invention, this invention provides a vehicle drive system, comprising an engine, a drive wheel, a continuously variable transmission provided between the engine and the drive wheel, a motor connected to either one of the engine and drive wheel, a battery electrically connected to the motor, a sensor which detects an accelerator depression amount, a sensor which detects a vehicle speed, a sensor which detects an engine rotation speed, and a controller functioning to compute a target drive power based on the accelerator depression amount and vehicle speed, set a target engine power according to the target drive power, set a reserve drive power for vehicle acceleration, compute a minimum needed power by subtracting an available discharge power of the battery from a value obtained by adding the reserve drive power to the target engine power, compute a best fuel cost-performance rotation speed based on the target engine power and the best fuel cost-performance power characteristics of the engine, compute a minimum needed rotation speed based on the minimum needed power and the maximum power characteristics of the engine, compare the best fuel cost-performance rotation speed and minimum needed rotation speed, and select the larger as the target input rotation speed of the transmission, compute the maximum power of the engine based on the engine rotation speed, compare the target engine power with the maximum engine power, and select the smaller as a final value of the target engine power, control the torque of the motor based on the target drive power and the final value of the target engine power, and control the torque of the engine based on the engine rotation speed and the final value of the target engine power.
The details as well as other features and advantages of this invention are set forth in the remainder of the specification and are shown in the accompanying drawings.